I looked at AMD Windows 10 CHIPSET Package for B550 and it does include several Windows 7 Drivers including USB.
But you can't run the Windows 10 CHIPSET in Windows 7. Don't know if you run it under "Compatibility" if it will run or not.
So you can try and see if by unpacking using 7-Zip, the AMD Windows 10 CHIPSET package and then using Device Manager "Update Driver" to guide it to the folder where you unpacked the AMD CHIPSET Package.
Hopefully Device Manager will scan the entire folder and update or install the correct USB Driver that you need.
Here are all the Windows 7 Drivers in the Windows 10 CHIPSET Package according to its Info.xml file:
If you can't update the Windows 7 drivers using Device Manager than I suggest you go to Seven Forums and find out where you can download those drivers.
NOTE: Have you tried your Motherboard's AMD CHIPSET Driver package? Maybe they have a Windows 7 CHIPSET Package to download.
